Greeks vs. Persians

The Persians likely looked down on the Greeks because as a whole, the Greeks valued intellectual pursuits over military ones, while the Persians placed warriors in high regard.  With the exception of Sparta, the Greek city-states focused on technological and philosophical ideas.  They had militaries, but not the desire to conquer the world.  However, the Greeks did spread throughout the Mediterranean through colonization.  The Persians could have thought of Greece the same as Egypt, which they managed to overcome.  Also, Greece was not zoroastrian, and the Persians likely looked down on Greece for its pantheon of gods.